Aerosol spraying

ABSTRACT

A method of improving the spraying of liquid droplets from a spray device onto a surface which method comprises imparting a unipolar charge to the said liquid droplets by double layer charging during the spraying of the liquid droplets from the spray device, the unipolar charge being at a level such that the said droplets have a charge to mass ratio of at least ±1×10 −4  C/kg, whereby the charged droplets of the liquid are mutually repelled thereby increasing the spread of the droplets from a central spray line extending from the head of the spray device and avoiding coalescence of the droplets, thus providing a more even coverage of the surface which is to be sprayed. In particular, the method enables liquid droplets to be sprayed onto a surface which is obscured by all object located between the surface and the spray device.

The present invention relates to a method of spraying aerosols which arecreated during the spraying process from a liquid composition locatedwithin a container by forcing the liquid through a suitable spray headattached to the container from which it emerges in aerosol form.

The present invention is particularly concerned with the formation ofaerosols using domestic aerosols spray devices. Such devices may containliquid compositions capable of forming aerosols for use in a wide rangeof applications including disinfectants, paints, antiperspirants,deodorants and insecticides. Reference will be made hereinafter todisinfectant applications but it should be appreciated that the presentinvention may be of use in connection with many other aerosolapplications.

Dispersion of compositions from an aerosol spray device is not ideal asthe spray of liquid droplets emerging from the aerosol device isgenerally propelled by sufficient force to enable the liquid dropletsonly to travel more or less in a straight line with a relatively smallspread angle for a distance perhaps of the order of 1 meter or more.This is because of the restrictions on the design of the spray headincluding the outlet orifice. During their travel, the liquid dropletswill, until they lose momentum, tend to maintain a straight line pathalthough some attraction may take place between individual liquiddroplets causing coalescence between one or more droplets, therebypossibly reducing the spread of droplets from a central spray lineextending from the spray head.

In the case of a disinfectant product, the aim of the user is to sprayan aerosol disinfectant from the spray device in a manner such that theliquid droplets make contact with microorganisms, typically in the formof bacteria, viruses or fungal spores. Microorganisms tend to accumulateon or adjacent to surfaces which are relatively difficult to access, forexample, surfaces located behind the pedestals, handles and rims ofsinks, showers, toilets or wash basins. A conventional aerosol spraydevice, when operated so that the spray is directed in the generaldirection of these inaccessible areas, will result in the liquiddroplets encountering the surfaces of objects which lie between thespray device and the inaccessible areas. Accordingly, the liquiddroplets will impinge on these objects and will never make contact withthe desired target areas. Furthermore, it is difficult to ensure that aspray of, for example, a disinfectant composition will reach into all ofthe corners, crevices, pits, hollows and other areas of a surface whichare difficult to access. With conventional techniques it is thereforedifficult to sterilise the surfaces of operating theatres, hospitalwards and other institutions.

We have now developed an improved method of spraying compositions whichenables the liquid droplets of the compositions to cover and targetsurfaces more effectively and, in particular, which enables the dropletsto target obscured or partly obscured surfaces.

According, to the present invention there is provided a method ofimproving the spraying of liquid droplets from a spray device onto asurface which method comprises imparting a unipolar charge to the saidliquid droplets by double layer charging during the spraying of theliquid droplets from the spray device, the unipolar charge being at alevel such that the said droplets have a charge to mass ratio of atleast +/−1×10⁻⁴ C/kg, whereby the charged droplets of the liquid aremutually repelled thereby increasing the spread of the droplets from acentral spray line extending from the head of the spray device andavoiding coalescence of the droplets, thus providing a more evencoverage of the surface which is to be sprayed.

In a particular aspect of the present invention there is provided amethod of spraying liquid droplets from a spray device onto a surfacewhich is obscured by an object located between the surface and the spraydevice so that liquid droplets travelling in a straight line from thespray device to the surface will impinge on said object, the methodcomprising imparting a unipolar charge to the said liquid droplets bydouble layer charging during the spraying of the liquid droplets fromthe spray device, the unipolar charge being at a level such that thesaid droplets have a charge to mass ratio of at least +/−1×10⁻⁴ C/kg,whereby at least some of the droplets are caused to travel in a pathwhich avoids the object and impinges on the obscured surface.

It will be understood that the object which obscures the surface whichit is desired to spray may be a part of the same article as the articlepossessing the said surface. The invention is thus applicable to thetreatment of three dimensional articles where certain surfaces areobscured from View along a particular line of sight. Accordingly, atleast a part of the obverse surfaces of articles may be sprayed withliquid droplets using the method of the invention.

It is preferred that the unipolar charge which is imparted to the liquiddroplets is generated solely by the interaction between the liquidwithin the spray device and the spray device itself as the liquid isexpelled therefrom. In particular, it is preferred that the manner inwhich a unipolar charge is imparted to the liquid droplets does not relyeven partly upon the connection of the spray device to any externalcharge inducing device, such as a source of relatively high voltage, orinternal charge inducing device, such as a battery. With such anarrangement, the spray device is entirely self-contained, making itsuitable for use both in industrial, institutional and domesticsituations.

Preferably, the spray device is a domestic pressure-spraying devicedevoid of any electrical circuitry but which is capable of being handheld. Typically such a device has a capacity in the range of from 10 mlto 2000 ml and can be actuated by hand, or by an automatic actuatingmechanism. A particularly preferred domestic device is a hand-heldaerosol can.

Preferably, therefore the droplet charge to mass ratio of at least+/−1×10⁻⁴ C/kg is imparted to the liquid droplets as a result of the useof an aerosol spray device with at least one of the features of thematerial of the actuator, the size and shape of the orifice of theactuator, the diameter of the dip tube, the characteristics of the valveand the formulation of the composition contained in the aerosol spraydevice being chosen in order to achieve the said droplet charge to massratio by double layer charging imparting the unipolar charge to thedroplets during the actual spraying of the liquid droplets from theorifice of the aerosol spray device.

As a result of the method of the present invention surfaces which arenormally difficult to access or inaccessible to the spray from anaerosol spray device can be contacted by the spray, thereby renderingmany operations much more manageable. By way of example, microorganismssuch as bacteria located in areas which are normally difficult to accessmay be easily eliminated in accordance with the method of the invention.

The method of the present invention may be used, for example, to sprayan obscured surface of a sink, shower, toilet, washbasin, chair leg, ahandle of a door, cupboard or refrigerator, a part of a human body, or apart of a plant with a liquid composition such as a disinfectant orantimicrobial composition. The method of the invention may also be usedto improve the targeting of certain products to their intendeddestination. For example, more effective spraying of hairsprays,antiperspirants, body sprays, waxes and polishes, oven cleaners,starches and fabric finishes, shoe and leather ware products, glasscleaners, paints, lubricants, house plant sprays, antistickcompositions, insecticides, herbicides, fungicides, biopesticides,disinfectants, and various other household, institutional, professionalor industrial products may be achieved, with a reduction in the amountof product required to be used and a reduction in the amount of theproduct which does not impinge upon the target.

The result of the method of the invention is achieved because of theunipolar charge imparted to the liquid droplets of the aerosol spray.This charge has two effects. First, the droplets, since they carried thesame polarity charge, are repelled one from another. Accordingly, thereis little or no coalescence of the droplets. Rather they tend to spreadout to a great extent during their path of travel, thereby following acurved path. In addition, if the repulsive forces from the charge withinthe droplets is greater than the surface tension force of the droplets,the charged droplets are caused to fragment into a plurality of smallercharged droplets (exceeding the Rayleigh limit). This process continuesuntil either the two opposing forces are equalised or the droplet hasfully evaporated.

Secondly, the liquid droplets carrying the unipolar charge are attractedto grounded conducting surfaces such as wood, metal or ceramics byinteraction with their image charge. If non-conducting surfaces carry anopposite polarity charge to that of the liquid droplets, then attractionwill equally be effected. Those liquid droplets that are attracted tothe surface are able to cover the surface much more evenly than withuncharged droplets as at the same time as they are being attracted tothe surface, they are also repelling one another.

Accordingly, those liquid droplets which proceed past the obscuringobject and are not travelling in a direction towards the target surface,will tend to be attracted towards the target surface and therefore theirpath of travel follows a curve terminating at the surface.

It will be appreciated that the two effects can be cumulative such thatsome at least of the liquid droplets will follow a significantly curvedpath of travel from the aerosol spray device, past the obscuring objectand into contact with the target surface.

The liquid composition which is sprayed into the air using the aerosolspray device is preferably a water and hydrocarbon mixture, or emulsion,or a liquid which is converted into an emulsion by shaking the sprayingdevice before use, or during the spraying process.

Whilst all liquid aerosols are known to carry a net negative or positivecharge as a result of double layer charging, or the fragmentation ofliquid droplets, the charge imparted to droplets of liquid sprayed fromstandard devices is only of the order of +/−1×10⁻⁸ to 1×10⁻⁵ C/kg.

The invention relies on combining various characteristics of the designof an aerosol spray device so as to increase the charging of the liquidas it is sprayed from the aerosol spray device.

A typical aerosol spray device comprises:

1. An aerosol can containing the composition to be sprayed from thedevice and a liquid or gaseous propellant.

2. A dip tube extending into the can, the upper end of the dip tubebeing connected to a valve;

3. An actuator situated above the valve which is capable of beingdepressed in order to operate the valve; and

4. An insert provided in the actuator comprising an orifice from whichthe composition is sprayed.

A preferred aerosol spray device for use in the present invention isdescribed in WO 97/12227.

It is possible to impart higher charges to the liquid droplets bychoosing aspects of the aerosol device including the material, shape anddimensions of the actuator, the actuator insert, the valve and thediptube and the characteristics of the liquid which is to be sprayed, sothat the required level of charge is generated as the liquid isdispersed as droplets.

A number of characteristics of the aerosol system increase double layercharging and charge exchange between the liquid formulation and thesurfaces of the aerosol system. Such increases are brought about byfactors which may increase the turbulence of the flow through thesystem, and increase the frequency and velocity of contact between theliquid and the internal surfaces of the container and valve and actuatorsystem.

By way of example, characteristics of the actuator can be optimised toincrease the charge levels on the liquid sprayed from the container. Asmaller orifice in the actuator insert, of a size of 0.45 mm or less,increases the charge level of the liquid sprayed through the actuator.The choice of material for the actuator can also increase the chargelevel on the liquid sprayed from the device with material such as nylon,polyester, acetal, PVC and polypropylene tending to increase the chargelevel. The geometry of the orifice in the insert can be optimised toincrease the charge level on the liquid as it is sprayed through theactuator. Inserts which promote the mechanical break-up of the liquidgive better charging.

The actuator insert of the spray device may be formed from a conducting,insulating, semi-conducting or static-dissipative material.

The characteristics of the dip tube can be optimised to increase thecharge level in the liquid sprayed from the container. A narrow diptube, of for example about 1.27 mm internal diameter, increases thecharge level on the liquid, and the dip tube material can also bechanged to increase charge.

Valve characteristics can be selected which increase the charge to massratio of the liquid product as it is sprayed from the container. A smalltailpiece orifice in the housing, of about 0.65 mm, increases productcharge to mass ratio during spraying. A reduced number of holes in thestem, for example 2×0.50 mm, also increase product charge during spray.The presence of a vapour phase tap helps to maximise the charge level, alarger orifice vapour phase tap of, for example, about 0.50 mm to 1.0 mmgenerally giving higher charge level.

Changes in the product formulation can also affect charging levels. Aformulation containing a mixture of hydrocarbon and water, or anemulsion of an immiscible hydrocarbon and water, will carry a highercharge to mass ratio when sprayed from the aerosol device than either awater alone or hydrocarbon alone formulation.

It is preferred that an aerosol spray composition of use in the presentinvention comprises an oil phase, an aqueous phase, a surfactant and apropellant.

Preferably the oil phase includes C₉-C₁₂ hydrocarbon which is preferablypresent in the composition in the amount of from 2 to 10% w/w.

Preferably the surfactant is glyceryl oleate or a polyglycerol oleate,preferably present in the composition in an amount of from 0.1 to 1.0%w/w.

Preferably the propellant is liquified petroleum gas (LPG) which ispreferably butane, optionally in admixture with propane. The propellantmay be present in an amount of from 10 to 90% w/w depending upon whetherthe composition is intended for spraying as a “wet” or as a “dry”composition. For a “wet” composition, the propellant is preferablypresent in an amount of from 20 to 50% w/w, more preferably in an amountof from 30 to 40% w/w.

The liquid droplets sprayed from the aerosol spray device will generallyhave diameters in the range of from 5 to 100 micrometers, with a peak ofdroplets of about 40 micrometers. The liquid which is sprayed from theaerosol spray device may contain a predetermined amount of a particulatematerial, for example, fumed silica, or a predetermined amount of avolatile solid material, such as menthol or naphthalene.

A can for a typical aerosol spray device is formed of aluminium orlacquered or unlacquered tin plate or the like. The actuator insert maybe formed or, for instance, acetal resin. The valve stem lateral openingmay typically be in the form of two apertures of diameters 0.51 mm.

The present invention will now be described, by way of examples only,with reference to the accompanying drawings, in which:

FIG. 1 is a diagrammatic cross section through an aerosol sprayingapparatus in accordance with the invention;

FIG. 2 is a diagrammatic cross section through the valve assembly of theapparatus of FIG. 1;

FIG. 3 is a cross section through the actuator insert of the assemblyshown in FIG. 2;

FIG. 4 shows the configuration of the bore of the spraying head shown inFIG. 3 when viewed in the direction A;

FIG. 5 shows the configuration of the swirl chamber of the spraying headshown in FIG. 3 when viewed in the direction B; and

FIG. 6 illustrates composition tests and results showing the efficacy ofthe present invention.

Referring to FIGS. 1 and 2, an aerosol spray device in accordance withthe invention is shown. It comprises a can 1, formed of aluminium orlacquered or unlacquered tin plate or the like in conventional manner,defining a reservoir 2 for a liquid 3 having a conductivity such thatdroplets of the liquid can carry an appropriate electrostatic charge.Also located in the can is a gas under pressure which is capable offorcing the liquid 3 out of the can 1 via a conduit system comprising adip tube 4 and a valve and actuator assembly 5. The dip tube 4 includesone end 6 which terminates at a bottom peripheral part of the can 1 andanother end 7 which is connected to a tailpiece 8 of the valve assembly.The tailpiece 8 is secured by a mounting assembly 9 fitted in an openingin the top of the can and includes a lower portion 10 defining atailpiece orifice 11 to which end 7 of the dip tube 4 is connected. Thetailpiece includes a bore 12 of relatively narrow diameter at lowerportion 11 and a relatively wider diameter at its upper portion 13. Thevalve assembly also includes a stem pipe 14 mounted within the bore 12of the tailpiece and arranged to be axially displaced within the bore 12against the action of spring 15. The valve stem 14 includes an internalbore 16 having one or more lateral openings (stem holes) 17 (see FIG.2). The valve assembly includes an actuator 18 having a central bore 19which accommodates the valve stem 14 such that the bore 16 of the stempipe 14 is in communication with bore 19 of the actuator. A passage 20in the actuator extending perpendicularly to the bore 19 links the bore19 with a recess including a post 21 on which is mounted a spraying headin the form of an insert 22 including a bore 23 which is incommunication with the passage 20.

A ring 24 of elastomeric material is provided between the outer surfaceof the valve stem 14 and, ordinarily, this sealing ring closes thelateral opening 17 in the valve stem 14. The construction of the valveassembly is such that when the actuator 18 is manually depressed, iturges the valve stem 14 downwards against the action of the spring 15 asshown in FIG. 2 so that the sealing ring 24 no longer closes the lateralopening 17. In this position, a path is provided from the reservoir 2 tothe bore 23 of the spraying head so that liquid can be forced, under thepressure of the gas in the can, to the spraying head via a conduitsystem comprising the dip tube 4, the tailpiece bore 12, the valve stembore 16, the actuator bore 19 and the passage 20.

An orifice 27 (not shown in FIG. 1) is provided in the wall of thetailpiece 8 and constitutes a vapour phase tap whereby the gas pressurein the reservoir 2 can act directly on the liquid flowing through thevalve assembly. This increases the turbulence of the liquid. It has beenfound that an increased charge is provided if the diameter of theorifice 27 is at least 0.76 mm.

Preferably the lateral opening 17 linking the valve stem bore 16 to thetailpiece bore 12 is in the form of 2 orifices each having a diameter ofnot less than 0.51 mm to enhance electrostatic charge generation.Further, the diameter of the dip tube 4 is preferably as small aspossible, for example, 1.2 mm, in order to increase the charge impartedto the liquid. Also, charge generation is enhanced if the diameter ofthe tailpiece orifice 11 is as small as possible eg not more than about0.64 mm.

Referring now to FIG. 3, there is shown on an increased scale, a crosssection through the actuator insert of the apparatus of FIGS. 1 and 2.For simplicity, the bore 23 is shown as a single cylindrical aperture inthis Figure. However, the bore 23 preferably has the configuration, forinstance, shown in FIG. 4. The apertures of the bore 23 are denoted byreference numeral 31 and the aperture-defining portions of the bore aredenoted by reference numeral 30. The total peripheral length of theaperture-defining portions at the bore outlet is denoted by L (in mm)and a is the total area of the aperture at the bore outlet (in mm²) andthe values for L and a are as indicated in FIG. 4. L/a exceeds 8 andthis condition has been found to be particularly conductive to chargedevelopment because it signifies an increased contact area between theactuator insert and the liquid passing there through.

Many different configurations can be adopted in order to produce a highL/a ratio without the cross-sectional area a being reduced to a valuewhich would allow only low liquid flow rates. Thus, for example it ispossible to use actuator insert bore configurations (i) wherein the boreoutlet comprises a plurality of segment-like apertures (with or withouta central aperture); (ii) wherein the outlet comprises a plurality ofsector-like apertures; (iii) wherein the aperture together form anoutlet in the form of a grill or grid; (iv) wherein the outlet isgenerally cruciform; (v) wherein the apertures together define an outletin the form of concentric rings; and combinations of theseconfigurations. Particularly preferred are actuator insert boreconfigurations wherein a tongue like portion protrudes into the liquidflow stream and can be vibrated thereby. This vibrational property maycause turbulent flow and enhanced electrostatic charge separation of thedouble layer, allowing more charge to move into the bulk of the liquid.

Referring now to FIG. 5, there is shown a plan view of one possibleconfiguration of swirl chamber 35 of the actuator insert 22. The swirlchamber includes 4 lateral channels 36 equally spaced and tangential toa central area 37 surrounding the bore 23. In use, the liquid drivenfrom the reservoir 2 by the gas under pressure travels along passage 20and strikes the channels 36 normal to the longitudinal axis of thechannels. The arrangement of the channels is such that the liquid tendsto follow a circular motion prior to entering the central area 37 andthence the bore 23. As a consequence, the liquid is subjected tosubstantial turbulence which enhances the electrostatic charge in theliquid.

The following Example illustrates the ability of liquid dropletsprojected from an aerosol spray device to “wrap around” an obscuringobject in order to reach a surface located behind that object.

EXAMPLE 1

In this Example, a Dettox Antibacterial Room Spray aerosol spray device(Reckitt and Colman Products Limited) was used. The device was testedboth in its unmodified form and with an electrostatic charge imparted tothe aerosol spray by means of the application of a high voltage to theaerosol can during actuation thereof. Referring to FIG. 6 of theaccompanying drawings, FIG. 6A illustrates the arrangement using anunmodified aerosol spray device, whereas FIG. 6B illustrates the use ofthe aerosol spray device modified by the application of a high voltageto the aerosol can.

A solution containing the bacteria Serratia marcescens was sprayed froma pump-action spray onto a sheet of transparent plastic (Item 101 ofFIGS. 6C and 6D) thereby leaving a biofilm on this sheet. The sheet wasleft to air dry for a few minutes. It was then wrapped around an earthedcylinder 103 which was 5.5 cm in diameter. The two ends of the plasticsheet were secured at the rear of the cylinder with double-sidedadhesive tape, such that the plastic sheet was continuous around thetarget cylinder. An aerosol can 105 of Dettox Antibacterial Room Spraywas held in a plastic actuating cradle (not shown), positioned 60 cammechanism from the front face of the cylinder target 103 with the targetpositioned in the centre of the aerosol plume resulting from actuationof the aerosol can 105. A two second spray of the Dettox product wasmade, delivering approximately 2.0 grams. The plastic film was thenremoved from the target, and placed biofilm-side down onto an agarmedium of the same size, such that there were no air bubbles between theplastic sheet and the agar. The bacteria were transferred in this way,and the agar was placed in an incubator overnight in order for bacterialcolonies to be grown. This procedure was repeated with the DettoxAntibacterial Room Spray aerosol carrying a high electrostatic charge of−1×10⁻⁴ C/kg. This was achieved by connecting the can to a high voltagegenerator and applying −10 KV to the aerosol can during spraying.

After 24 hours the growth of bacterial colonies on the growth medium wasassessed and photographed. The resulting photographs are illustrated inFIG. 6C (obtained from the arrangement of FIG. 6A) and FIG. 6D (obtainedfrom the arrangement of FIG. 6B). The bacterial colonies appear as darkareas or dark spots in FIG. 1C and FIG. 1D. The centre of each rectanglewas the area located on the front surface of the target and was directlyand well treated with the aerosol spray. The areas at the edges of therectangles were located on the rear surface of the target andaccordingly could not be contacted by liquid droplets travelling in astraight line from aerosol can (105) to target (103). FIG. 6C shows thatliquid droplets from the unmodified aerosol spray device only contact,and therefore kill, bacteria on the front of the target which weredirectly in the spray path, but not bacteria on the rear of the target.In contrast, liquid droplets from the modified aerosol spray devicewhich were electro-statically charged, reached the rear of the cylinderand few bacteria survived in this area, i.e. the aerosol spray reachedparts of the target which were not directly in the spray path.

What is claimed is:
 1. A method of improving the spraying of liquid droplets from a spray device onto a surface which method comprises imparting a unipolar charge to the said liquid droplets by double layer charging during the spraying of the liquid droplets from the spray device, the unipolar charge being at a level such that the said droplets have a charge to mass ratio of at least +/−1×10⁻⁴ C/kg, whereby the charged droplets of the liquid are mutually repelled thereby increasing the spread of the droplets from a central spray line extending from the head of the spray device and avoiding coalescence of the droplets, thus providing a a more even coverage of the surface which is to be sprayed.
 2. A method of spraying liquid droplets from a spray device onto a surface which is obscured by an object located between the surface and the spray device so that liquid droplets travelling in a straight line from the spray device to the surface will impinge on said object, the method comprising imparting a unipolar charge to the said liquid droplets by double layer charging during the spraying of the liquid droplets from the spray device, the unipolar charge being at a level such that the said droplets have a charge to mass ratio of at least +/−1×10⁻⁴ C/kg, whereby at least some of the droplets are caused to travel in a path which avoids the object and impinges on the obscured surface.
 3. A method as claimed in claim 1 or claim 2, wherein the spray device is an aerosol spray device.
 4. A method as claimed in any one of the preceding claims wherein the spray device contains an emulsion.
 5. A method as claimed in any one of the preceding claims wherein the liquid droplets have a diameter in the range of from 5 to 100 micrometers.
 6. A method as claimed in any one of the preceding claims wherein the unipolar charge is imparted to the liquid droplets solely by the interaction between the liquid and the spray device, without any charge being imparted thereto from an internal or external charge inducing device.
 7. A method as claimed in any one of the preceding claims wherein the droplets charge to mass ratio of at least +/−1×10⁻⁴ C/kg is imparted to the liquid droplets as a result of the use of an aerosol spray device with at least one of the features of the material of the actuator, the size and shape of the orifice of the actuator, the diameter of the dip tube, the characteristics of the valve and the formulation of the composition contained in the aerosol spray device being chosen in order to achieve the said droplet charge to mass ratio by double layer charging imparting the unipolar charge to the droplets during the actual spraying of the liquid droplets from the orifice of the aerosol spray device.
 8. A method as claimed in any one of the preceding claims wherein the spray device contains a composition comprising an oil phase, an aqueous phase, a surfactant and a propellant.
 9. A method as claimed in claim 8 wherein the oil phase includes a C₉-C₁₂ hydrocarbon.
 10. A method as claimed in claim 9 wherein the C₉-C₁₂ hydrocarbon is present in the composition in an amount of from 2 to 10% w/w.
 11. A method as claimed in any one of claims 8 to 10 wherein the surfactant is glyceryl oleate or a polyglycerol oleate.
 12. A method as claimed in any one of claims 8 to 11 wherein the surfactant is present in the composition in an amount of from 0.1 to 1.0% w/w.
 13. A method as claimed in any one of claims 8 to 12 wherein the propellant is liquified petroleum gas.
 14. A method as claimed in claim 13 wherein the propellant is present in the composition in an amount of from 30 to 40% w/w.
 15. A method as claimed in claim 2 wherein the object which obscures the surface which it is desired to spray is part of the same article as the article possessing the said surface.
 16. A method as claimed in claim 2 or claim 15 wherein the obscured surface which is sprayed in accordance with the present invention is an obscured surface of a sink, shower, toilet, wash basin, a chair leg, a handle of a door, cupboard or refrigerator, a part of a human body, or a part of a plant. 